Flying roll change (flying splice) in paper mills or the like is a common technique for replacing an old, almost fully unwound roll of paper by a new roll without having to stop the machines, which run at high speed. This is done using double-sided self-adhesive tapes, so-called tabs, which on the one hand are highly adhesive and highly tacky but on the other hand, owing to their water-soluble self-adhesive compositions and paper backings, do not cause disruption in the paper machine when the paper wastes are reused. These tabs are bonded in complicated bonding patterns to the start of the web, a procedure requiring experienced personnel, with little time remaining for the entire procedure owing to the increasing speeds of the machines.
Although this technology is well established, it is not without certain disadvantages. Thus, experienced personnel are required, the procedure is intrinsically hectic, and the bonds are also relatively thick: the maximum total thickness of the bond originates from two paper plies and the tear adhesive tape in between, plus any fixing labels. It is a concern on the part of the paper industry to reduce this bond thickness to a minimum.
For traditional methods of bonding in flying splice there are various products on the market, called tabs, which in addition to a paper backing feature a water-soluble self-adhesive composition coated on both sides. Adhesive tapes of this kind are on the market, inter alia, under the name tesafix (Beiersdorf).
The prior art describes diverse adhesive tapes for such purposes. For instance, EP 418 527 A2 discloses a method of preparing a roll of printing material in web form for automatic roll changes and an adhesive strip suitable for that method. DE 40 33 900 A1 also describes an adhesive tape suitable for a splice site. A disadvantage, however, are adhesive regions which lie exposed after the splice method has been implemented.
The nonadhesive masking of otherwise exposed adhesive areas is taught by U.S. Pat. No. 5,702,555 for more static loadings of a securement of a roll start, while DE 196 32 689 A2 discloses an adhesive tape of this kind for dynamic loading during the splicing process, the paper backing of said tape cleaving and masking the adhesives with its residues.
Also of this kind is an adhesive tape according to DE 196 28 317 A1, likewise for a splicing method. This adhesive tape carries, on its nonadhesive reverse face, a double-sided adhesive tape (6) which has a readily cleaving paper backing (7) which cleaves (7a, 7b, FIG. 3) during the splicing method and masks the respective adhesives. This double-sided adhesive tape (6) ends at the side with one side of the paper backing (2); it is, therefore, arranged along one of the long edges of the adhesive tape.
DE 199 02 179 A1 also discloses an adhesive tape for this application, where, in order to avoid breaks during flying splice, an adhesive tape laminated on with paper backing (P2) of cleavable paper is disposed with an inset, specifically at a certain distance (V) from the long edge (LK) of the adhesive tape.
In practise, even these adhesive tapes exhibit disadvantages, primarily because a flying splice is unsuccessful and instead ends as a break, without any evident reason for this.
It was an object of the invention to provide a remedy here.
This object is achieved by an adhesive tape for flying splice, comprising    a) a first backing having a top side, a bottom side and two long edges, with a water-soluble self-adhesive coating on the top side,    b) a double-sided adhesive tape, having a cleavable paper backing with two long edges and coated on both sides with a water-soluble self-adhesive composition, adhesively bonded to the bottom side of said first backing, wherein,    c) at least one of said two long edges of said double-sided adhesive tape has a jagged cut.
Admittedly, jagged cutting as such is known and is employed in particular in order to provide products equipped accordingly with hand tearability. Such as in the case of textiles or in the case of adhesive tapes; cf. DE 43 18 277 C1. This property of the easier tearability by hand would, however, have necessarily led right away from the inventive use of a jagged cut, since at the high speeds and high forces which occur during flying splice unwanted and possibly premature breaks would have to be considered likely, particularly since DE 199 02 179 A1 expressly recommends “clean cut edges” (p. 2, line 54).
However, it has been found that a flying splice with the adhesive tapes of the invention is more reliable on account of the very low initial cleaving force at the tip of the jag and the force which increases continuously as the area of the jag increases. Breaks, accordingly, are effectively prevented.
The cleavable paper advantageously has a significantly lower cleavage resistance than a paper backing, which has to absorb tensile forces.
Suitable cleavable backings (or cleavable systems), in particular as cleavable papers, include for example the following papers or paper composite systems:                Duplex papers: these papers are standard commercial products and are used, for example, in the production of filter materials and wall coverings.        Readily cleaving papers: the cleavage energy is adjusted by way of the consolidation of the paper fiber structure. The lower the consolidation, the lower the cleavability.        
Additionally suitable paper systems include, for example, machine-finished papers calendered on one side or else highly filled kraft papers.                sized paper systems: the cleavability is adjusted by way of the chemistry of the adhesive size. The size ought not to have penetrated substantially into the paper.        It is also possible to use a cleaving system in accordance with DE 198 41 609 A1.        
The amount by which the cleavable material is set in, or the distance from the long edge, should be about 0.5 to 15 mm, in particular 1–7 mm, and very particularly 1.5 mm–3.5 mm.
A variety of cleavable paper systems are suitable as the cleavable paper, such as                Duplex papers (papers laminated together in a defined manner; the process of cleavage proceeds extremely homogeneously, with no stress peaks produced as a result, for example, of inhomogeneous consolidation. These papers are used for the production of wall coverings and filters.        Readily cleavable paper systems        Highly consolidated papers sized together in a defined way (→paper with a high cleavage strength). Sizing may be carried out, for example, using starch, starch-containing derivatives, wallpaper pastes based on methylcellulose (Methylan®, Henkel KGaA, Düsseldorf) or else based on polyvinyl alcohol derivatives.        The width of the backing of cleavable paper is preferably 3–20 mm, especially 6–12 mm.        
Suitable self-adhesive compositions include all basic types of pressure-sensitive adhesive, particularly                Acrylates (water-soluble and water-insoluble)        Natural rubber compositions, synthetic rubber compositions        and dispersions thereofThe splice method, in this case the bonding operation using the splicing tape, may in particular take place in such a way that the adhesive tape is bonded to the running web at right angles.        
The drawings show a diagram of an adhesive tape of the invention and its use and is therefore intended to illustrate the invention by way of example.
On cleavage strength and its measurement, refer to DE 199 02 179 A1, also with regard to the materials which can be used, especially papers and adhesives.
Generally, the cleavage strength of the cleavable backing is from 20 to 70 cN/cm. In a particular embodiment the cleavage strength is 22 to 60 cM/cm.
Also suitable are embodiments as described in DE 198 30 674, DE 198 30 673 and DE 196 28 317 A1, but also in accordance with DE 196 32 689. Those documents are therefore expressly incorporated by reference. Particular preference, however, is given to an embodiment according to DE 199 02 179 A1.
The purpose of the text below is to describe the invention in more detail with reference to an example, but without wishing to subject it to any unnecessary restriction as a result.